As Meb Keflezighi was passing runners late in the London Olympic Marathon in August, he noticed a green singlet ahead. He figured his next target must be South African.

As he closed in, he saw the runner was from Brazil and recognized Marilson Gomes dos Santos, an old foe and friend. Keflezighi had mixed feelings. As he moved from fifth to fourth in the final half mile, he told dos Santos, “Good job, keep going.”

“I wanted to encourage him, but at the same time make sure I got to the finish first,” says Keflezighi, who finished in 2:11:06, four seconds ahead of dos Santos. “If any of those [top three] guys got busted [for doping], I wanted to be the one who gets on the medal stand.”

Keflezighi, 37, and dos Santos, 35, have done a lot of racing together over the years. They’ll be back at it November 4 in the ING New York City Marathon, a race each has won.

Their first matchup occurred in NYC in 2006 when dos Santos was the surprise winner and Keflezighi struggled to a 21st-place finish with a case of food poisoning. “I was like, ‘Doggone it. That should have been me,’” Keflezighi says with a laugh.

Dos Santos won New York again in 2008 as Keflezighi sat out the race, recovering from injuries. When they met again in NYC in 2009, Keflezighi won as dos Santos did not finish.

They renewed their rivalry in NYC in 2010 when Keflezighi finished sixth in 2:11:38, one place and 13 seconds ahead of dos Santos. Thanks to many races and enough close finishes over the years, they have struck up a relationship, communicating in English, Spanish, and Portuguese.

“He’s an excellent athlete and a very nice person,” says dos Santos with his agent, Luis Felipe Posso, acting as translator. “We compliment each other always before and after races. We are friendly with each other.”

They talked in the cafeteria at the Athletes’ Village at the London Games. “He went out of his way to come by and say hello,” Keflezighi says. “I appreciated that.”

Both were undertrained for London due to injury problems, yet both performed well.

“I respect him tremendously,” Keflezighi says of dos Santos. “He’s been a very consistent marathoner. He’s a smart competitor. I always depend on him to do well. When we’re in races, I think, “That’s the guy I have to keep my eye on.’”

You can say the same about Keflezighi. The two have other things in common: Both have long-time coaches—Bob Larsen for Keflezighi, Adauto Domingues for dos Santos—and both have run well late in their careers.

“It’s a result of two factors,” dos Santos says. “One is the experience of training throughout the years without many injuries. And the fact I don’t race that much. I don’t chase races every weekend. The combination has helped.”

Similarly, Keflezighi doesn’t over-race and is incredibly disciplined in his approach to training and recovery. “You work hard and pay attention to details,” he says. “I’m pretty sure he tries to get everything right because he wants to maximize his ability and not look back at his career with regret. We probably have the same trait.”

Could their rivalry last until 2016, when the Olympics will be held in Rio de Janeiro? Dos Santos is besieged by both fans and the press about his participation.

“I would love to do it,” he says. “It’s going to depend how I feel physically, how my body responds to the physical training and the mental part of things.”

Keflezighi has said that he’s 99-percent sure London was his last Olympics—but he hasn’t completely ruled out another attempt.

And he has another idea: “Maybe Marilson will invite me to Brazil if I don’t make the team so I can enjoy the hospitality of the Brazilians. That would be nice.”